Guar is a high molecular weight, water soluble galactomannan polysaccharide used in hydraulic fracturing processes. Like all hydraulic fracturing fluids, a guar-based fluid needs to maintain a sufficient viscosity to prevent proppant settling and to support transport of proppant into fractures. To achieve the required thickening of the fracturing fluid while minimizing the amount of guar, a crosslinking agent, such as borax can be used to crosslink guar molecules. These guar/borate crosslinked fluids can be pumped at pressures sufficient to crack the rock of the formation allowing penetration of the proppant and gel mixture into the fracture. Conventional guar/borate crosslinked fluids can be used in hydraulic fracturing processes at temperatures in the range from 100 deg F. (37.8 deg C.elsius (deg C.)) to 300 deg F. (148.9 deg C.). However, the viscosity of guar/borate crosslinked fluids can show reversibility in response to a number of influences including mechanical shear, pH, and temperature. In addition, these fluids can lose viscosity under an increase in pressure. The viscosity of guar/borate crosslinked fluids can be reduced under pressure greater than 2500 psi due to the loss of some or all of the viscosity contributed by the crosslinkers. It is understood that the crosslinking between cis-hydroxyl groups and borate is reversed when the pressure is increased, thus causing the reduced viscosity. The reduction in viscosity can happen almost instantaneously after the pressure is increased.
One way to minimize the pressure response of the guar/borate crosslinked fluids is to use a high polymer loading of the base guar polymer. Another option to minimize the pressure response of the guar/borate crosslinked fluids is to use a high dose of crosslinkers. However, these options can result in an initial viscosity that causes excessive friction during pumping of the fracturing fluid and can result in a gel that cannot be broken after hydraulic fracturing is complete. Both of these options result in an increase in costs of the fracturing fluid.